Influence of fibroblast growth factor on phosphorylation and activity of a 34 kDa lipocortin‐like protein in bovine epithelial lens cells

Abstract

We examined the effect of basic fibroblast growth factor (FGF) on phosphorylation and lipocortin-like activity of the 34 kDa protein present in the basal membrane of epithelial peripheral cells which initiate growth and differentiation in the bovine lens. We found that: (i) the 34 kDa protein possesses anti-phospholipase A 2 (PL/%) activity of lipocortin; (ii) in response to FGF, the anti-PLA 2 activity of this protein is enhanced whereas its phosphorylation is markedly decreased. It is suggested that the 34 kDa protein might represent an important biological activity in controlling FGF induction of growth and differentiation in the adult eye lens.

Activation of phosphotyrosine phosphatase activity is associated with decreased differentiation in adult bovine lens

“…It is of note that the phosphorylation of calpactins has been suggested to regulate the level of membrane-cytoskeleton interactions (Powell and Glenney, 1987;Schlaepfer and Haigler, 1987;Crompton et al, 19881, a spatial framework thought to be involved in dramatic morphological alterations that take place as the equatorial lens epithelium begins to elongate into fiber cells (Beebe et al, 1980;Ramaekers and Bloemendal, 1981;Zelenka, 1983;Beebe and Cerrelli, 1989). It is also of note that the anti-PLAZ activity of calpactins appears to be dependent on their phosphorylation state in the equatorial epithelium (Blanquet et al, 1988(Blanquet et al, , 1990. In addition, studies have indicated that calpactins can be found in the nucleus and contain DNAbinding motifs, purportedly participating in the regulation of transcriptional activity (Jindal et al, 1991;Raynal et al, 1992;Boyko et al, 1994).…”

“…Although the physiological roles of calpactins in general still remain obscure, it was suggested that these proteins might be involved in the regulation of growth and differentiation (William et al, 1988;Jindal et al, 1991;Talian and Zelenka, 1991;Boyko et al, 1994;Reutelingsperger et al, 1994). Interestingly, preliminary observations in our laboratory suggested that a bFGF-stimulatable PTPase activity confined to the equatorial epithelium of bovine lens appears to act predominantly on a calpactin-like protein (Blanquet et al, 1988(Blanquet et al, , 1990. The possibility that the phosphorylation statute of this protein may be involved in modulating fiber differentiation opens therefore an exciting area of research.…”

“…Molecular weights of proteins are shown in kilodaltons. liminary studies, we described the effects of bFGF on the phosphorylation and phospholipase A, (PLA, ) activity of lipocortin of a substrate of 34 kD, when assayed from central and equatorial epithelia of adult bovine lens (Blanquet et al, 1988(Blanquet et al, , 1990. In particular, in contrast to the strong activation observed when this substrate was obtained from the central epithelium, a decreased phosphorylation and PLA, activity occurred when it was derived from the equatorial epithelium.…”

A dimeric form of lipocortin-1 in human placenta

“…In intact cells they are substrates for the EGF [14][15][16][17] and insulin [18] receptor kinases and for pp60V"src (see [10,19] for references), and have been shown to translocate from cytoplasm to the membrane upon Ca21 treatment [20]; yet the key biological functions of the proteins are unclear. In assays in vitro, phosphorylation decreases their Ca2" affinity, decreases their ability to bind membranes, and neutralizes the phospholipase-inhibitory activity [21][22][23][24][25]. Because alterations in the N-terminal segment affect these processes [26,27], an important step in understanding the roles of these two proteins is to understand the state of the N-terminal segment and of its interactions.…”

Role of lipocortin I in the glucocorticoid induction of the terminal differentiation of a human squamous carcinoma

“…Phosphorylation alters calcium and phospholipid binding properties in vitro Powell and Glenney, 1987); however, the key biological effects of this modification are unclear. While many studies have demonstrated that phosphorylation of the lipocortins eliminates their PLA2 inhibitory activity, in all instances where phosphoamino acid analysis was performed, the critical site of phosphorylation was localized on serineithreonine residues (Hirata, 1981;Takagi and Ichikawa, 1987;Blanquet et al, 1988).…”